Stud welding apparatus

ABSTRACT

A weldable fastener for supporting insulation adjacent to a surface and apparatus for welding the fastener are provided. The insulation fastener is specifically designed for applying insulating material to the outer surface of a wall of a cryogenic container, which walls are commonly made of aluminum. The fastener includes, in the preferred form, an aluminum stud having a weldable end and a recess at the opposite end. A strong plastic-glass fiber rod, which is preferably made by a pultrusion process, is affixed in the recess of the stud and extends outwardly therefrom, coaxially with the stud. After the insulation is placed over the rod and stud and against the surface, a suitable clip or washer is applied over the end of the rod to hold the insulation in place. The apparatus for welding the stud to the surface includes a stud welding tool which operates by a known end-welding technique. The tool has a chuck leg terminating in an offset member holding a chuck at one side of the tool. The tool also has an offset welding foot which locates a welding ferrule at the one side of the tool and in alignment with the chuck. The chuck has a through passage to enable the rod of the weldable stud to extend past the one side of the tool when the stud is in position in the chuck and ready for welding.

This is a division, of application Ser. No. 663,056 filed Mar. 2, 1976,now U.S. Pat. No. 4,085,307.

This invention relates to a fastener particularly for insulation and toapparatus for affixing the fastener to a surface.

The insulation fastener according to the invention is particularlydesigned for use with cryogenic containers which commonly have aluminumwalls to enable them to withstand the very low temperatures to whichthey are subjected. Thick layers of insulation are located against theouter surfaces of the container walls. The insulation fastener accordingto the invention enables the insulation to be applied to the outersurfaces of the walls of such containers rapidly and efficiently. Thenew fastener includes a metal stud having a weldable end which can beaffixed by an end welding technique to the outer surface of thecontainer wall. The stud is preferably of aluminum so as to becompatible with the container material, and preferably has a conicalconfiguration at the weldable end terminating in a smalloutwardly-extending tip. The opposite end of the stud has a central,elongate recess therein which receives a strong rod of low conductingmaterial, the rod extending beyond the outer surface of the insulatinglayer. The rod is held in the recess of the stud by being crimpedtherein and, to provide a positive mechanical engagement, the rodpreferably has a shallow groove to receive the inwardly-extendingsurfaces of the crimps. The rod, in a preferred form, is made of glassfibers impregnated and encased in resin and formed by a pultrusionprocess. A flat clip or washer is placed on and mechanically engagedwith the outer end of the rod to hold the insulation in place againstthe container wall.

In order to weld the preassembled combination fastener to the wall ofthe cryogenic container, a special welding tool is employed. The toolincorporates an offset chuck adapter member which is affixed to an outerend of a chuck leg of the tool and extends transversely to hold a chuckparallel to but spaced from the chuck leg. The chuck has a passageextending completely therethrough with the low conducting rod of thefastener extending through the chuck and to the side of the tool whenthe stud is held in the outer end of the chuck by resilient fingersthereof. The welding tool also has a welding foot carrying a gas shieldaffixed to another offset member and aligned with the chuck and thepassage therethrough. A ceramic ferrule is also carried by the weldingfoot to contain the molten metal formed as the stud is welded to thesurface.

It is, therefore, a principal object of the invention to provide animproved insulation fastener and apparatus for affixing the fastener toa surface.

Another object of the invention is to provide a preassembled insulationfastener for cryogenic containers, which fastener includes an aluminumstud having a weldable end and a recessed end and a rod of lowconducting material affixed mechanically in the recess.

A further object of the invention is to provide apparatus for welding anelongate fastener, which apparatus includes an offset member forpositioning a chuck to one side of the tool with the chuck having apassage extending completely therethrough to receive a portion of theelongate fastener.

Many other objects and advantages of the invention will be apparent fromthe following detailed description of preferred embodiments thereof,reference being made to the accompanying drawings, in which:

FIG. 1 is a fragmentary view in transverse cross section taken through awall of a cryogenic container and layers of insulation adjacent thereto,and showing a fastener assembly welded in position and holding theinsulating layers in place;

FIG. 2 is a greatly enlarged, fragmentary view in longitudinal crosssection taken through a stud and a rod of the fastener of FIG. 1;

FIG. 3 is a view in transverse cross section showing a mechanicalconnection between the stud and the rod, taken along the line 3--3 ofFIG. 2;

FIG. 4 is a fragmentary view on a smaller scale, with parts broken awayand with parts in cross section, of a modified insulation fastener;

FIG. 5 is a somewhat schematic view in elevation, with parts broken awayand with parts in cross section, of apparatus for welding the insulationfastener, with the fastener being shown in a position to be welded;

FIG. 6 is a transverse view on an enlarged scale taken along the line6--6 of FIG. 5;

FIG. 7 is a fragmentary view in longitudinal cross section taken alongthe line 7--7 of FIG. 6;

FIG. 8 is an enlarged front view of a welding foot and a gas shield ofthe apparatus of FIG. 5; and

FIG. 9 is a view in transverse cross section taken along the line 9--9of FIG. 8.

Referring particularly to FIG. 1, a cryogenic container or the like hasa wall 20 to which insulation 22 is attached by an insulation fastener24. The insulation 22 is positioned contiguous to an outer surface 26 ofthe wall 20 and can take a variety of forms. As shown, the insulation 22includes four relatively rigid layers 28 of insulating material with athinner layer or blanket 30 of more yieldable insulating materiallocated between two of the layers 28. This provides a degree ofresiliency or tolerance for the overall thickness of the insulation 22.It is to be understood, however, that the invention is not to be limitedto being applicable to any specific type, thickness, shape, or number oflayers of insulating material or even to insulating material at all.

The insulation fastener 24 basically includes a composite assembly of aweldable stud 32 and a rod or rod-like elongate member 34 of lowconducting material. A suitable clip or washer 36 is placed over andaffixed to the outer end of the rod 34 after the stud 32 is welded tothe wall 20 and the insulation 22 is in place. The insulation 22 can, inat least some instances, be affixed to the container by impaling theinsulating layers 28 and 30 on the rod 34 and the stud 32. If theinsulation is not of a nature that it can be so impaled, it can be boredout to form a passage having a diameter larger than that of the stud andthe rod and placed thereover. A foamable material can then be insertedthrough a suitable opening in the clip 24 and foamed in situ in thepassage to provide a continuous thermal barrier around the entirecontainer.

Referring particularly to FIG. 2, the stud 32 is of metal and ispreferably of aluminum when used in cryogenic applications since thewall 20 of the cryogenic container also usually is of aluminum towithstand the very low temperatures encountered. The stud 32 has aweldable end 38 which includes an outer relatively shallow conicalsurface 40 and a central tip 42. When the stud 32 is welded to thesurface 26 of the wall 20, the tip 42 and at least most of the conicalportion 40 are fused, leaving a weld bead 43 (FIG. 1).

An end 44 of the stud 32 opposite the weldable end 38 has acentrally-located, axially-extending, elongate recess 46. Crimps 48 areformed at intermediate portions of the elongate recess 46 and produceinwardly-extending ridges 50. The rod 34 is received in the recess 46prior to the crimping and extends outwardly from the stud 32 in aco-axial manner. A portion of the rod 34 received in the recess is cutaway to form an annular, wide, shallow groove 52 into which the ridges50 of the crimps 48 extend when the crimps are formed with the rod inplace. Preferably, the length of the crimps 48 is such that the ends ofthe ridges 50 bear against shoulders 54 and 56 which are formed in therod 34 at the ends of the shallow groove 52. This prevents anypossibility of longitudinal movement of the rod 34 relative to the stud32.

In the form shown in FIGS. 1 and 2, the outer end of the rod 34 has aplurality of narrow, annular grooves 58 formed therein to receivefingers or tangs 60 of the clip 36. The tangs are sufficiently resilientthat the clip 36 can be pushed onto the end of the rod 34 to hold theinsulating layers 28 and 30 securely in place, with the tangs 60 thenbeing mechanically engaged in the appropriate one of the grooves 58 ofthe rod. If desired, the grooves 58 can be eliminated and the tangs 60can be shaped and sized such as to simply bite into the outer surface ofthe rod 56 at any position where the clip 36 is placed, to resistoutward movement of the clip relative to the rod.

The rod 34 is of low conducting material and, in a preferred form, ismade of longitudinally-extending glass fibers impregnated and encasedwith resin. Such a rod preferably is made by a pultrusion process whichforms a very strong rod and yet one having low conductivity. With thelongitudinally-extending fibers of the rod, the annular grooves 58 areformed rather than a continuous helical thread which would tend todestroy the outer fibers of the pultruded rod. The specific clipemployed with the rod does not form part of this invention.

A slightly modified insulation fastener embodying the invention isindicated at 62 in FIG. 4. The fastener 62 includes the end-weldablestud 32 and a modified pultruded rod 64 extending rearwardly therefrom.The rod has a wide, shallow groove 66 corresponding to the groove 52 atthe end received in the recess 46 of the stud 32 and, in this instance,also has an annular, wide, shallow groove 68 near the outer end. A metalextension 70 is located at the outer end of the rod 64 and has a recess72 which receives this end of the rod. Crimps 74 are formed atintermediate portions of the recess 72 and form inwardly-extendingridges 76. The ridges 76 are received in the shallow recess 68 toprovide a secure mechanical connection between the rod 64 and theextension 70. With the extension 70 being made of metal, an outer thread78 can be machined at the end thereof. A clip similar to the clip 36,but with appropriately formed tangs or fingers, can then be threadedthereon. The clip is turned onto the thread 78 until it is snug againstthe outer surface of the insulation 22.

Installation of both of the fasteners 24 and 64 is relatively simplebecause the components are preassembled. The stud 32 and the rod 34 orthe stud 32, the rod 64, and the extension 70, are supplied in one pieceas complete assemblies. The stud 32 is then simply welded to the surface26 of the wall 20 and the insulation placed over the rod 34 or the rod64 and the extension 70, with a clip then added in a quick and efficientmanner.

The stud 32 is welded to the wall 20, in a preferred form, by adrawn-arc welding technique. In order to weld the long fastener 24 or62, a special welding tool is employed, such as is shown in FIGS. 5-9.For this purpose, a tool 80 includes means for retracting the stud fromthe workpiece, means for holding the stud in the retracted position, andmeans for subsequently moving the stud toward and against the workpiece.A power source and controls initiate a low current between the stud andthe workpiece as the stud is withdrawn, in order to form a pilot arc.The controls also determine when the stud is plunged back toward theworkpiece, and when a higher current is imposed on the pilot arc toestablish a main welding arc between the stud and the workpiece. Themain welding arc fuses the tip 42 and at least a portion of the conicalend 40, along with a portion of the workpiece. The molten metal portionsthen join and solidify when the stud engages the workpiece at the end ofthe plunge stroke, thereby providing a secure weld therebetween.

The stud welding tool 80 is basically of a known design and includes amain body or housing 82 of suitable dielectric material. A chuck leg 84extends forwardly of the body 82 and, within the body, terminates in awelding cable head or terminal 86. The head 86 is connected to a liftingrod 88 which extends rearwardly through a movable core 90. A liftinghook 92 is attached to the core 90 and engages a lifting ring 94 whenmoved rearwardly.

The inner diameter of the lifting ring 94 slightly exceeds the outerdiameter of the lifting rod 88 so that the rod can move longitudinallyrelative to the ring when the ring is held perpendicular thereto. Thering is normally so held by a lifting ring spring 96 which urges thering against a rear annular extension of a stop plate 98. The plate 98,in turn, is held against shoulders (not shown) within the body 82 by amain plunge spring 100 located between the plate 98 and the head 86.With this design, the lifting rod 88 can be moved back somewhat when theend of the stud 32 is pressed against the surface 26 of the wall 20prior to being welded. However, when the ring 94 is moved by the liftinghook 92 and the core 90 to a canted position, further retraction of thecore 90 also causes the lifting rod 88 to retract the same distance asthe core. Consequently, all of the studs to be welded will be retracteda uniform, predetermined distance from the workpiece during the liftingor retraction stroke, even though their length may differ somewhat sothat some are pushed back more than others when initially pressedagainst the workpiece.

The movable core 90 is retracted when current is supplied throughsuitable leads 102 to a lifting or holding coil 104. The extent of therearward movement of the core, which determines the distance the stud isretracted, is determined by the position of an adjustable core stop 106.Current for the pilot arc and the main welding arc are supplied to thechuck leg 84 through a cable 108 suitably connected to the head 86.

Because of the length of the fastener 24 and specifically the rod 34, itis not feasible to hold the stud 32 directly in front of the chuck leg84, as has heretofore been conventional in the art. Therefore, inaccordance with the invention, an offset chuck adapter or member 110 isaffixed to the end of the chuck leg 84 and extends transversely thereof.As shown, the offset adapter is received on a threaded end 112 of thechuck leg 84 and is held in position by two adjustable nuts 114 and 116.At a location spaced from the chuck leg 84, the offset adapter 110 has athreaded opening 118 (FIG. 7) which receives a threaded end 120 of achuck 122. The chuck 122 has longitudinally-extending slots 124 whichform resilient fingers or tines 125, there being three in this instance.The tines 126 have shoulders 128 near their extremities which abut andback up the outer end of the stud 32. The chuck 122 also has a shoulderflange 130 which abuts the offset adapter 110. The flange 130 can beengaged by a wrench for removal of the chuck from the offset adapter 110for replacement, as is commonly required with such chucks fromtime-to-time.

Of particular importance, the chuck 122 has a passage 132 extendingcompletely therethrough from the ends of the tines 126 to the extremityof the threaded end 120. This enables the rod 34 to extend completelythrough the chuck and the offset adapter 110 when the stud 32 is firmlyengaged in the chuck. The distance from the front of the tool body 82 tothe offset adapter 110 is less than the length of the rod 34. However,the offset adapter 110 is sufficiently long that the rod 34 can extendback to one side of the tool body 82, as shown in FIG. 5. Hence, withthis arrangement, the tool 80 can accommodate the long fastener 24 andeffectively weld the stud 32 without having to assure unwieldydimensions and design.

In order to weld the elongate fastener 62, or a similar fastener with anenlarged outer end, the top of the chuck 122 and the top of the offsetadapter 110 can have slots therein. The width of the slots exceed thediameter of the rod 64 so that the rod can be inserted in the slots andthen retracted to move the stud 32 into the chuck with the end of thestud abutting the shoulders 128 of the tines 126. The slotted chuck canbe held in the slotted adapter by a setscrew rather than try thethreaded connection to assure that the slots will be aligned when thechuck and adapter are assembled.

The welding tool 80 also has two welding foot legs 134 extendingforwardly of the body 82 and mounted therein in an adjustable manner, asis known in the art. At the extremities of the legs 134 is an offsetwelding foot 136 which also extends transversely a substantial distancefrom the legs 134. The welding foot 136 has an opening 138 therein(FIGS. 8 and 9) which is aligned with the chuck 122 and through whichthe stud 32 centrally extends. The opening 138, in this instance, has aprotective liner 140 and the foot has means in the form of an O-ring142, in this instance, to yieldably hold a spark shield member shownspecifically in the form of a welding ferrule 144. The welding ferrule144 is of a ceramic construction as is well known in the art andsurrounds the weldable end of the stud 32 during the welding operationto contain the molten metal and prevent weld splatter on adjacentcomponents.

In this instance, the O-ring 142 is held between the front of the offsetfoot 110 and a gas shield member 146 mounted at the front of the foot136 by suitable fasteners (not shown). The shield is also held by anextension 148 which extends through the foot and is threadedly-engagedby a fitting 150 which receives a gas supply line. The gas shield 146 isparticularly advantageous when used with the aluminum ferrule to preventa weak, porous weld from resulting. The gas, preferably an inert gassuch as helium or argon, from the supply line attached to the fitting150 flows past a valve 152 which opens when a valve stem 154 and the gasshield are pressed against the workpiece. The gas then flows through anannular manifold 156 around the opening 138 and through suitable ports158 to an annular chamber 160 surrounding the ferrule 144 and the stud.After the stud is welded and the foot 136 is removed from the workpiece,the valve 152 closes again until the next weld.

With other studs not requiring the gas atmosphere, the ferrule 144 canbe suitably held in the offset welding foot 136 in a known manner withthe offset foot 136 again being of sufficient length to align theferrule and the stud held by the chuck 122 and the offset adapter 110.

Various modifications of the above-described embodiments of theinvention will be apparent to those skilled in the art, and it is to beunderstood that such modifications can be made without departing fromthe scope of the invention, if they are within the spirit and the tenorof the accompanying claims.

I claim:
 1. A welding tool for welding an elongate metal stud to a workpiece, said stud having an elongate rod-like member extending from one end thereof, the rod-like member having a transverse dimension smaller than a corresponding dimension of the stud, said welding tool comprising a welding tool body, a chuck leg extending forwardly from said body, an offset member of conductive material affixed to an end of said chuck leg and extending transversely beyond one side of said tool, a chuck affixed to said offset member, said chuck having a passage extending completely therethrough, said passage having a shoulder therein for engaging and backing up an end of the stud from which the elongate rod-like member extends, said chuck having resilient fingers for engaging an outer surface of the stud adjacent the end engaged by said shoulder, said chuck positively preventing rearward movement of the stud in said chuck, a welding foot, a spark shield member carried by said welding foot for holding a ferrule, said spark shield member having resilient means for engaging the ferrule, and means carried by said welding tool body for positioning said spark shield member in alignment with said chuck and spaced forwardly thereof away from said tool body. 